The invention can be said to be a direct further development of the art which is described in U.S. Pat. No. 4,708,714. The content of this patent is therefore included in the present description.
The known art is primarily intended for treatment of blood plasma which is alternately mixed with another liquid and whereby the mixture ratio is measured optically. Certain difficulties have manifested themselves through operation in the measuring instrument and also through variations in optical absorbency in the plasma during patient treatment. Variations can be caused by, for example, the patient eating. Employed measuring instruments have therefore often had to be recalibrated. Because of the measuring errors an unnecessarily large quantity of plasma has sometimes been discarded instead of being returned to the patient.
The present invention has therefore as its object to minimize the plasma loss in the system according to the American patent and simultaneously provide a safe, preferably automatic, calibration of measuring instruments used therefore.